JP5082790B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system, and more particularly to a fuel cell system having a diluter that mixes and dilutes anode offgas and cathode offgas discharged from a fuel cell stack.

  In recent years, since there is little influence on the environment, an attempt has been made to mount a fuel cell stack on an automobile or vehicle. The fuel cell stack supplies, for example, a fuel gas such as hydrogen to the anode side of the fuel cell, supplies an oxidant gas containing oxygen, such as air, to the cathode side, and takes out necessary power by an electrochemical reaction through the electrolyte membrane. Is.

  The cathode offgas when the oxidant gas supplied to the cathode side is discharged from the fuel cell stack includes reaction product water generated by an electrochemical reaction. On the other hand, the reaction product water that has passed through the electrolyte membrane is also included in the anode off-gas when the fuel gas supplied to the anode side is discharged from the fuel cell stack.

  The anode off gas is sent to the diluter by opening a purge valve provided in the middle of a pipe connecting the anode off gas outlet of the fuel cell stack and the diluter at a predetermined timing. Cathode off-gas is also sent from the fuel cell to the diluter via piping. In the diluter, the anode off gas is mixed with the cathode off gas, diluted, and then discharged to the outside. At this time, the reaction product water contained in each of the cathode offgas and the anode offgas is also discharged together.

  For example, in Patent Document 1, an open / close valve is provided in each of a fuel gas supply line for supplying fuel gas to a fuel cell and an exhaust fuel gas line for discharging exhaust fuel gas (anode offgas) from the fuel cell. A fuel cell system is disclosed in which these on-off valves are closed when operation is stopped.

JP 2002-216823 A

  However, the fuel cell system disclosed in Patent Document 1 does not have a diluter that dilutes and discharges the exhaust fuel gas, and therefore an on-off valve provided in the exhaust fuel gas line when the fuel cell is operated is provided. When a failure occurs in the open state, the high-concentration fuel gas present in the fuel gas flow path (including the flow path in the fuel cell) on the downstream side of the on-off valve on the supply line is directly discharged out of the system. There is a risk that.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a fuel cell system having a diluter that dilutes anode off gas with cathode off gas and exhausts the fuel cell, which can prevent high concentration fuel gas contained in anode off gas from being exhausted outside the system. To provide a system.

A fuel cell system according to the present invention includes a fuel cell that generates electricity by an electrochemical reaction between a fuel gas supplied to the anode side and an oxidant gas supplied to the cathode side, and an anode off-gas and a cathode off-gas discharged from the fuel cell. a diluter for exhausting by mixing dilute, and on-off valve provided in the anode off-gas flow path between the fuel cell and the diluter, and provided in the exhaust downstream side of the dilution vessel exhaust cutoff valve A humidifier that is provided downstream of the diluter in the exhaust direction and collects water contained in the anode off-gas and the cathode off-gas and uses it to humidify the oxidant gas, and an open / close valve is open. And a control unit that executes control to close the exhaust shut-off valve when an operation failure occurs.

  According to this configuration, the exhaust cutoff valve is installed on the downstream side of the diluter in the exhaust direction, and the exhaust cutoff valve is closed when the on-off valve is open and malfunctions, so that high concentration fuel gas is generated. It is possible to prevent exhausting out of the system as it is.

  The fuel cell system according to the present invention further includes a gas supply device that supplies an oxidant gas to the cathode side of the fuel cell, and the control unit increases the rotation speed of the gas supply device after the exhaust shut-off valve is closed. It is preferable to execute the control.

  According to this configuration, when the anode off-gas boosted in the diluter by closing the exhaust shut-off valve flows back to the fuel cell via the cathode off-gas channel, the cathode of the fuel cell is increased by increasing the rotation speed of the gas supply unit. By forcibly supplying the oxidant gas to the side, the oxidant gas for reaction can be provided for the high-concentration fuel gas in the backflow anode offgas.

  Furthermore, the fuel cell system according to the present invention further includes a gas pressure regulating valve provided in a cathode off gas flow path between the fuel cell and the diluter, and the control unit opens the gas pressure regulating valve after closing the exhaust cutoff valve. It is preferable to carry out the adjustment.

  According to this configuration, when the anode off-gas boosted in the diluter by closing the exhaust shut-off valve flows backward toward the fuel cell through the cathode off-gas flow path, the opening of the gas pressure regulating valve is adjusted. The high-concentration fuel gas contained in the backflow anode offgas can be suppressed to an amount commensurate with the reaction oxidant gas supplied to the fuel cell. As a result, it is possible to prevent the backflowed high-concentration fuel gas from being blown through the fuel cell and released into the atmosphere.

  Embodiments according to the present invention will be described below in detail with reference to the drawings. In this description, specific shapes, materials, and the like are examples for facilitating the understanding of the present invention, and can be appropriately changed in accordance with the application, purpose, specifications, and the like.

  FIG. 1 is a diagram showing a schematic configuration of a fuel cell system 10 according to an embodiment of the present invention. The fuel cell system 10 includes a fuel cell stack 12 as a fuel cell, a purge valve (open / close valve) 14, an air pressure regulating valve (gas pressure regulating valve) 16, a diluter 18, an air cutoff valve (exhaust cutoff valve) 28, and a control unit. 38 etc. are comprised.

  The fuel cell stack 12 is formed by laminating a plurality of unit cells sandwiched by placing separators on both outer sides of an MEA (Membrane Electrode Assembly) in which catalyst electrode layers are arranged on both sides of an electrolyte membrane. The fuel cell stack 12 supplies a fuel gas such as hydrogen to the anode side, supplies an oxidant gas containing oxygen, such as air, to the cathode side, generates power by an electrochemical reaction through the electrolyte membrane, and takes out necessary power. It has a function.

  Hydrogen gas is supplied from a fuel tank 20 through an injector 22 to a gas inlet on the anode side of the fuel cell stack 12. The injector 22 has a function of adjusting the hydrogen gas from the fuel tank 20 to an appropriate pressure and flow rate and ejecting the hydrogen gas. A pressure gauge 26 is connected to the pipe 24 extending from the injector 22 to the fuel cell stack 12. The pressure gauge 26 detects the pressure of hydrogen gas supplied to the fuel cell stack 12.

  The anode-side outlet of the fuel cell stack 12 is connected to a diluter 18 via an anode off-gas passage 15, and a purge valve 14 is provided in the anode off-gas passage 15. The purge valve 14 is controlled to be temporarily switched to the open state by the control unit 38 at a predetermined timing. Further, when the purge valve 14 is in the closed state, the anode off-gas discharged from the anode side outlet is boosted by a circulation booster 27 that is a pump, for example, and returned to the anode side inlet of the fuel cell stack 12 for reuse. It is supposed to be. While circulating in this way, in the anode off-gas, the concentration of hydrogen, which is a fuel gas, is reduced by the consumption of an electrochemical reaction, while the concentration of the electrochemical reaction product water and nitrogen passing through the electrolyte membrane from the cathode side decreases. Will be included. The diluter 18 mixes and dilutes the anode off gas containing hydrogen, water, etc. discharged from the fuel cell stack 12 with the cathode off gas discharged from the cathode side outlet of the fuel cell stack 12, and then exhausts the anode off gas. is there.

  The diluter 18 is connected to the humidifier 30 via an air shutoff valve 28 provided on the downstream side in the exhaust direction. Electricity for the fuel cell stack 12 and the diluter 18 is provided between the diluter 18 and the air shut-off valve 28 or between the air shut-off valve 28 and the humidifier 30 by a portion connected by an insulating pipe such as a rubber hose. Mechanical insulation can be taken. When the air shut-off valve 28 is in the open state, the exhaust gas exhausted from the diluter 18 passes through the generated water to the porous body built in the humidifier 30 when passing through the humidifier 30, and is not shown in the figure. It is discharged to the outside via a silencer (also called a muffler).

  In the present embodiment, the air shut-off valve 28 is disposed between the diluter 18 and the humidifier 30, but is not limited thereto, and is disposed downstream of the humidifier 30 in the exhaust direction. May be.

  The fuel cell system 10 also includes an oxidant gas source 32 as a supply source of an oxidant gas, for example, oxygen supplied to the cathode side of the fuel cell stack 12. The oxidant gas source 32 can actually use an atmosphere containing oxygen. The air from the oxidant gas source 32 is pressurized by an air compressor (gas supply machine) 34 and is appropriately humidified when passing through the humidifier 30 before being supplied to the cathode side inlet of the fuel cell stack 12. It is made to do. A flow meter 36 is installed between the oxidant gas source 32 and the air compressor 34. The flow meter 36 detects the amount of air supplied to the cathode side of the fuel cell stack 12.

  In the present embodiment shown in FIG. 1, the oxidant gas source 32 and the air compressor 34 are provided on the opposite side of the fuel tank 20 with respect to the fuel cell stack 12, but the present invention is not limited to this. The oxidant gas source 32 and the air compressor 34 may be installed on the same side as the fuel tank 20 with respect to the fuel cell stack 12. In this way, there is an advantage that the air supply path from the air compressor 34 to the humidifier 30 can be shortened. Further, instead of the air compressor 34, for example, another gas supply machine such as a pump may be used.

The cathode side outlet of the fuel cell stack 12 is connected to a diluter 18 via a cathode offgas flow path 17, and an air pressure regulating valve 16 is provided in the cathode offgas flow path 17. The air pressure regulating valve 16, also called a back pressure valve, is a valve having a function of adjusting the gas pressure at the cathode side outlet to adjust the flow rate of air to the fuel cell stack 12. A valve capable of adjusting the effective opening can be used. Cathode off-gas discharged from the cathode side outlet is used as a diluent gas for diluting as hydrogen concentration in the anode Doofugasu in diluter 18 becomes less than a predetermined concentration. Further, the cathode off gas includes water vapor and condensed water generated by an electrochemical reaction in the fuel cell stack 12.

  The control unit 38 controls the entire fuel cell system 10 and can be specifically configured by a CPU, a memory, and the like. Further, the control unit 38 can be configured as a part of an electronic control unit (ECU) that controls electrical control of the entire automobile.

  Each detection signal is input to the control unit 38 from the pressure gauge 26 and the flow meter 36. Further, from the control unit 38, the valve opening / closing control signal of the injector 22, the opening / closing control signal of the purge valve 14, the opening adjustment signal of the air pressure regulating valve 16, the opening / closing control signal of the air shutoff valve 28, and the rotation speed control of the air compressor 34. A signal or the like is output.

  Next, the operation and control of the fuel cell system 10 having the above-described configuration will be described. In the fuel cell stack 12, the air pressurized by the air compressor 34 from the oxidant gas source 32 is appropriately humidified by the humidifier 30 and then supplied to the cathode side inlet. On the other hand, the hydrogen gas ejected from the fuel tank 20 is adjusted to an appropriate pressure and flow rate by the injector 22 and then supplied to the anode side inlet of the fuel cell stack 12. In the fuel cell stack 12, oxygen and hydrogen in the supplied air are generated by an electrochemical reaction through the electrolyte membrane, and electric power is output.

  The cathode off gas discharged from the cathode side outlet of the fuel cell stack 12 is air containing water generated by an electrochemical reaction, and flows into the diluter 18 via the air pressure regulating valve 16. On the other hand, the anode off gas discharged from the anode side outlet of the fuel cell stack 12 is a gas containing unconsumed hydrogen and water generated by an electrochemical reaction, and while the purge valve 14 is in a closed state, While being boosted by the circulation booster 27, it is supplied again to the anode side inlet and circulates. When the purge valve 14 is temporarily switched to the open state at a predetermined timing, the anode off gas flows into the diluter 18 through the purge valve 14.

  In the diluter 18, the anode off gas is mixed and diluted with the cathode off gas and exhausted. Exhaust gas, which is a mixture of anode off gas and cathode off gas, flows into the humidifier 30 via the air shutoff valve 28. Therefore, water contained in the exhaust gas is captured and collected by the built-in porous body. The water collected in the porous body is used for humidifying the air supplied to the fuel cell stack 12. The exhaust gas that has passed through the humidifier 30 is discharged to the outside through the silencer.

  In the present embodiment, since the humidifier 30 is disposed on the downstream side of the diluter 18, the large humidifier 30 may not be accommodated in a fuel cell case (not shown) that accommodates the fuel cell stack 12 or the like. The height dimension of the fuel cell case can be reduced. This is advantageous for mounting the fuel cell case in a space below the vehicle floor.

  In addition, when the porous body in the humidifier 30 is dried for some reason, there is a possibility that cross leak occurs in which hydrogen in the exhaust gas is mixed into the air supplied to the cathode through the porous body. . In this case, when the cross leaked hydrogen is supplied to the cathode side of the fuel cell stack 12 together with air, water is generated by a catalytic reaction, and the water is contained in the cathode off gas and is supplied to the humidifier via the diluter 18. By reaching 30 and being collected, the dry state of the humidifier 30 can be reduced urgently.

  FIG. 2 is a control flowchart executed by the control unit 38. First, it is determined whether or not the purge valve 14 has an open failure, that is, whether or not it has malfunctioned in the open state (step S1). In this determination, when the pressure detected by the pressure gauge 26 does not reach the predetermined value P with respect to the valve opening time of the injector 22, it is determined that the purge valve 14 has failed to open.

  When it is determined that the purge valve 14 is open, the amount of hydrogen gas leakage is calculated based on the pressure difference ΔP between the predetermined value P and the value detected by the pressure gauge 26, the internal volume of the diluter 18, and the like. The At the same time, the amount of air required to dilute the hydrogen gas leakage to the extent that it can be exhausted is required, and this is necessary to supply the amount of air to the cathode side of the fuel cell stack 12. The rotation speed of the air compressor 34 is set as a target value.

  If it is determined that the purge valve 14 has failed to open, the injector 22 is immediately closed to stop the supply of hydrogen gas to the fuel cell stack 12, and the air shutoff valve 28 is closed (step S2).

  The high-concentration hydrogen gas that has flowed into the diluter 18 due to the open failure of the purge valve 14 is increased in the diluter 18 because the air shutoff valve 28 is closed and cannot flow to the humidifier 30 side. It becomes a state. Therefore, the high-concentration hydrogen gas can flow backward from the diluter 18 toward the cathode side outlet of the fuel cell stack 12 via the cathode offgas flow path 17 and the air pressure regulating valve 16. Therefore, control for increasing the rotation speed of the air compressor 34 is executed (step S3). As a result, by forcibly increasing the supply of air to the cathode side of the fuel cell stack 12, oxygen for reaction can be provided to the high-concentration hydrogen gas in the anode off-gas that has flowed backward.

  Further, the opening degree of the air control valve 16 is adjusted so as to obtain a backflow hydrogen gas flow rate that matches the air flow rate supplied to the cathode side (step S4). As a result, it is possible to prevent the high-concentration hydrogen gas that has flowed back through the fuel cell stack 12 and released into the atmosphere via the air compressor 34.

  Then, it is determined whether or not the rotational speed of the air compressor 34 has reached the target value (step S5), and steps S3 to S5 are repeatedly executed until the target value is reached. When it is determined that the rotation speed of the air compressor 34 has reached the target value, the air shut-off valve 28 is opened (step S6), and the cathode off gas composed of air containing the reaction product water and diluted hydrogen gas is removed. It is discharged to the outside through the diluter 18 and the humidifier 30.

  As described above, in the fuel cell system 10 of the present embodiment, the air shutoff valve 28 is installed on the downstream side of the diluter 18 in the exhaust direction, and the air shutoff valve 28 is closed when it is determined that the purge valve 14 is open. By doing so, it is possible to prevent high-concentration hydrogen gas from being exhausted out of the system as it is.

It is a schematic block diagram of the fuel cell system which is one Embodiment of this invention. It is a flowchart which shows the process in a control part.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Fuel cell system, 12 Fuel cell stack, 14 Purge valve, 15 Anode off-gas flow path, 16 Air pressure regulation valve, 17 Cathode off-gas flow path, 18 Diluter, 20 Fuel tank, 22 Injector, 24 Piping, 26 Pressure gauge, 27 Circulation booster, 28 Air shut-off valve, 30 Humidifier, 32 Oxidant gas source, 34 Air compressor, 36 Flow meter, 38 Control unit.

Claims (3)

A fuel cell that generates electricity by an electrochemical reaction between a fuel gas supplied to the anode side and an oxidant gas supplied to the cathode side, and a diluter that mixes and dilutes the anode off-gas and cathode off-gas discharged from the fuel cell and exhausts them. An open / close valve provided in the anode off-gas flow path between the fuel cell and the diluter, an exhaust cutoff valve provided downstream in the exhaust direction with respect to the diluter, and the exhaust direction with respect to the diluter And a humidifier that recovers water contained in the anode off-gas and the cathode off-gas and uses it to humidify the oxidant gas, and shuts off the exhaust when the on-off valve is in an open state And a control unit that executes control for closing the valve. The fuel cell system according to claim 1, wherein
A fuel cell further comprising a gas supply device for supplying an oxidant gas to the cathode side of the fuel cell, wherein the control unit executes control to increase the rotation speed of the gas supply device after the exhaust shut-off valve is closed. system. The fuel cell system according to claim 1 or 2,
A fuel cell, further comprising a gas pressure regulating valve provided in a cathode off-gas flow path between the fuel cell and the diluter, wherein the control unit adjusts the opening of the gas pressure regulating valve after the exhaust cutoff valve is closed. system.

Images